For the purification and analysis of proteins and peptides, chromatography is a well-known and widely used method. A number of different chromatographic principles are applied, among these ion exchange chromatography (IEC). The IEC principle includes two different approaches: anion exchange and cation exchange according to the charge of the ligands on the ion exchange resin. A conventional IEC purification process usually consists of one or more: equilibration sections, application or loading sections, wash sections, elution sections, and regeneration sections (cf. Remington's Pharmaceutical Sciences, Gennaro, ed., Mack Publishing Co., Easton, Pa., 1990, or Remington: The Science and Practice of Pharmacy, 19th Edition (1995)).
The main principle of elution in IEC in industrial purification processes is salt component gradients in an aqueous buffer solution at constant pH, either as step or linear gradients (cf. S. Bjørn and L. Thim, Activation of Coagulation Factor VII to VIIa, Res. Discl. No. 269, 564-565, 1986). Isocratic elution is possible, but seldom used. Organic solvents or modifiers have occasionally been added to the solutions to keep the protein or peptide on the desired form or just in solution (cf. K. H. Jørgensen, Process for Purifying Insulin, U.S. Pat. No. 3,907,676, Sep. 23, 1975; and J. Brange, O. Hallund and E. Sørensen, Chemical Stability of Insulin 5. Isolation, Characterisation and Identification of Insulin Transformation Products, Acta Pharm. Nord. 4(4), 223-232, 1992).
Glucagon-Like Peptide-1 (GLP-1) (cf. Schmidt et al. in Diabetologia 28 704-707, 1985) and analogues as well as derivatives thereof may be used in the treatment of diabetes, as disclosed in WO 98/08871. A GLP-1 peptide and related analogues are easily dissolved in aqueous solvents and kept in a monomized form. Traditional IEC purification of GLP-1 with salt gradients in aqueous solvents may, however, be problematic due to the lack of selectivity between a GLP-1 target moiety and related impurities.
WO 87/06941 (The General Hospital Corporation) disclose peptide fragments which comprises GLP-1(7-37) and functional derivatives thereof and to its use as an insulinotropic agent.
WO 90/11296 (The General Hospital Corporation) disclose peptide fragments which comprise GLP-1(7-36) and functional derivatives thereof and have an insulinotropic activity which exceeds the insulinotropic activity of GLP-1(1-36) or GLP-1(1-37) and to their use as insulinotropic agents.
WO 91/11457 (Buckley et al.) discloses analogues of the active GLP-1 peptides 7-34, 7-35, 7-36, and 7-37.
WO 98/08871 discloses GLP-1 derivatives in which a lipophilic substituent is attached to at least one amino acid residue. The lipophilic substituents are in particular long-chain groups containing e.g. 12-24 carbon atoms.
WO 98/08872 discloses GLP-2 derivatives in which a lipophilic substituent is attached to at least one amino acid residue. The lipophilic substituents are in particular long-chain groups containing e.g. 12-24 carbon atoms.
WO 96/32414 discloses GLP-2 analogues.
EP 0699686-A2 (Eli Lilly & Co.) discloses certain N-terminal truncated fragments of GLP-1 that are reported to be biologically active.
EP 0708179-A2 (Eli Lilly & Co.) discloses GLP-1 analogues and derivatives that include an N-terminal imidazole group and optionally an unbranched C6-C10 acyl group in attached to the lysine residue in position 34.